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Very Heavy Menstrual Flow

When periods are very heavy or you are experiencing “flooding” or passing big clots you have what doctors call menorrhagia. The purpose of this article is to define normal and very heavy menstrual bleeding, to explain what causes heavy flow, and to show what you yourself can do in dealing with heavy flow.

This, and the article called “Managing Menorrhagia—Effective Medical Treatments” for your doctor or health care provider, are to help you avoid surgeries for heavy flow (hysterectomy and endometrial ablation) if you can.

What is the normal menstrual flow?

In a randomly selected group of premenopausal women, the most common amount of menstrual flow (measured in a laboratory from all collected tampons and pads) was about two tablespoons (30 ml) in a whole period (1;2). However the amount of flow was highly variable—it ranged from a spot to over two cups (540 ml) in one period! Women who are taller, have had children and are in perimenopause have the heaviest flow (2). The usual length of menstrual bleeding is four to six days. The usual amount of blood loss per period is 10 to 35 ml. Each soaked normal-sized tampon or pad holds a teaspoon (5ml) of blood. That means it is normal to soak one to seven normal-sized pads or tampons (“sanitary products”) in a whole period.

How is Very Heavy Flow or Menorrhagia defined?

Officially, flow of more than 80 ml (or 16 soaked sanitary products) per menstrual period is considered menorrhagia. Most women bleeding this heavily will have a low blood count (anemia) or evidence of iron deficiency (1). In practice only about a third of women have anemia, so the definition of heavy flow can be adjusted to be more like nine to 12 soaked regular-sized sanitary products in a period (2).

What causes very heavy menstrual bleeding?

This is not clear. Heavy flow is most common in the teens and in perimenopause—both are times of the lifecycle when estrogen levels tend to be higher and progesterone levels to be lower. Progesterone is made by the ovaries after ovulation. However, even though you may be having regular periods, it doesn’t mean you are ovulating! The lining of the uterus or endometrium sheds during a period. Estrogen’s job is to makes the endometrium thicker (and more likely to shed) and progesterone makes it thinner. Therefore it is likely that heavy flow is caused by too much estrogen and too little progesterone. However, this has not been well shown.

The good news is that, in a large study of pre- and perimenopausal women, heavy flow was not caused by endometrial cancer. This means that a diagnostic test for cancer called a D & C (a surgical procedure in which the endometrium is scraped off) is not necessary (3). Heavy flow was most common and occurred in 20% of women ages 40-44 (3). In women ages 40 to 50, those with heavy flow commonly also have fibroids. However higher estrogen with lower progesterone levels causes both heavy bleeding and the growth of fibroids. Fibroids are benign tumors of fibrous and muscular tissue that grow in the muscle of the uterine wall; less than 10% come close to the endometrium and are called “submucus” fibroids. Only these rare fibroids could possibly influence flow. So fibroids are rarely the real cause for heavy flow and are not a reason to treat very heavy flow any differently.

Early in perimenopause when cycles are regular, approximately 25% of women will have at least one heavy period. Perimenopausal estrogen levels are higher and progesterone levels are lower (4;5). (See Perimenopause, the Ovary’s Frustrating Grand Finale.) Progesterone levels are lower because ovulation is less consistent and short luteal phases (the portion of the normal menstrual cycle from ovulation until the day before the next flow) with fewer than 10 days of progesterone are common in perimenopause (6).

Some rare reasons for heavy flow are an inherited problem with bleeding (like hemophilia), infection or heavy bleeding from an early miscarriage.

Can I figure out how much I’m bleeding?

The easiest way, knowing that one soaked, normal-sized sanitary product holds about a teaspoon of blood (= 5 ml), is to record the number you soak each day of your flow. Another very easy way to measure flow is to use a menstrual cup like DivaCup® that has markers for 15 and 30ml of blood loss. Keeping the Menstrual Cycle Diary or Daily Perimenopause Diary is a convenient way to assess the amount and timing of flow using either a count of soaked regular sized sanitary products (tampons or pads) or a measuring menstrual cup. (Note that less than half of all cups marketed world-wide have flow volume markings so look for one that has them). To accurately record the number of soaked sanitary products each day you need to recall the number you changed that were half full (let’s say three tampons and one pad) and multiply that (four X 0.5 = two) to give the number of fully soaked ones. A “maxi” or “super” tampon or pad holds about two teaspoons or 10ml of blood—therefore record each larger soaked sanitary product as a “2.” In addition, record your best judgment about the amount of flow where a “1” is spotting, “2” means normal flow, “3” is slightly heavy and “4” is very heavy with flooding and/or clots. If the number of soaked sanitary products totals 16 or more or if you are recording “4”s you have very heavy flow. To measure your flow using a menstrual cup with measurements, just add up the approximate amounts from each time you emptied it and record on the "# of pads/tampons" line.

What can I do for very heavy flow?

    1. Keep a record
      Make a careful record (see Diary, above) of your flow for a cycle or two. (Note—if flow is so heavy you start to feel faint or dizzy when you stand up, that is a reason to make an emergency doctor appointment.)
    2. Take ibuprofen
      Whenever flow is heavy, start taking ibuprofen, the over-the-counter anti-prostaglandin, in a dose of one 200mg tablet every 4-6 hours while you are awake. This therapy decreases flow by 25-30% and will also help with menstrual cycle-like cramps (7).
    3. Treat blood loss with extra fluid and salt
      Any time you feel dizzy or your heart pounds when you get up from lying down it is evidence that the amount of blood volume in your system is too low. To help that, drink more and increase the salty fluids you drink such as tomato or other vegetable juices or salty broths (like bouillon). You will likely need at least four to six cups (1-1.5 litre) of extra liquid that day.
    4. Take iron to replace what is lost with heavy bleeding
      If your doctor’s appointment is delayed or you realize that you have had heavy flow for a number of cycles, start taking one over-the-counter tablet of iron (like 35 mg of ferrous gluconate) a day. You can also increase the iron you get from foods—red meat, liver, egg yolks, deep green vegetables and dried fruits like raisins and prunes are good sources of iron. Your doctor will likely measure your blood count and a test called “ferritin” which tells the amount of iron you have stored in your bone marrow. If your ferritin is low, or if you ever have had a low blood count, continue iron daily for one full year to bring iron stores to normal.


What can my doctor do to evaluate heavy flow?

After asking you questions (and looking at your Diary or calendar records of flow) your doctor should do pelvic exam. If this is very painful, a culture should be taken to rule out infection that is a rare but serious cause for heavy flow. With the speculum a doctor see that bleeding is coming from the uterus and not from somewhere else.

What laboratory tests can my doctor order to assess heavy flow?

One of the consequences of heavy flow is loss of iron that is needed for hemoglobin to carry oxygen in red blood cells—low iron levels cause anemia (low hematocrit or hemoglobin which are commonly called “a low blood count”). Ferritin which shows how much iron is stored in the bone marrow could be ordered if heavy flow has been going on for a while, if you have started iron therapy, or you eat a vegetarian diet that tends to be low in iron. Ferritin can be low (because the savings account is empty) even if the hemoglobin and hematocrit are normal (the chequing account is not yet empty). Sometimes, heavy bleeding means a miscarriage so your doctor might order a pregnancy test.

What can my doctor do to treat heavy flow?

1. Progesterone or a stronger progestin therapy

Progesterone therapy makes sense because very heavy flow is associated with too much estrogen for the amount of progesterone. Progesterone’s job is to make the endometrium thin and mature—it antagonizes estrogen’s action that makes it thick and fragile. However, low doses given for two weeks or less a cycle are not effective (9). One study shows that very high doses of a strong progestin for 22 days a cycle decreased bleeding by 87%(10). I recommend starting treatment with oral micronized progesterone (Prometrium®) 300 mg at bedtime or medroxyprogesterone (10 mg) taken days 12-27 of the cycle. (See Cyclic Progesterone Therapy handout.). Always take progesterone for 16 days whenever you start it for heavy flow (even if flow starts before then). If needed, cyclic progesterone can be started right away, at any time of the cycle and will slow or stop the bleeding.

Heavy bleeding is so common in perimenopause that when a woman over 40 is traveling or will be in a remote place, she should ask her doctor for a 16-day supply of 300 mg of oral micronized progesterone (or 10mg medroxyprogesterone tablets) to take with her.

You are likely in very early perimenopause if flow is extremely heavy, you already have anemia or it has been going on for a long time progesterone needs to be taken daily for three months. Take oral micronized progesterone 300 mg at bedtime daily and continued, every day, for three months. Flow will become irregular but decrease in amount over time. After that you can take cyclic progesterone for a few more months. Also remember to always take ibuprofen on every heavy flow day.

As flow gets lighter the progesterone therapy can be decreased to a normal dose and taken days 14-27 of the cycle. In perimenopause, especially in women with a history of acne and unwanted facial hair (PCOS or anovulatory androgen excess) it is often necessary to treat with daily progesterone therapy for three months to also decrease the risks for endometrial cancer. Following that it is wise to use a cyclic treatment for days 12 through 27 of the cycle for six more months.

2. Oral contraceptive pills 
Although oral contraceptives are commonly used for heavy flow, they are not very effective, especially in perimenopause (8). Current “low dose” oral contraceptives contain levels of estrogen that, on average, are five times natural levels plus close to normal levels of progesterone-like medicines called progestins. Combined hormonal contraceptives (CHC) have not been shown to be effective for heavy flow perimenopause (13). In addition, they appear to prevent the important gain to peak bone mass during adolescence so should be avoided then. You would only choose to take CHC for heavy flow if you were not in perimenopause or adolescence and if you also needed contraception.

What other therapies can be added to progesterone if needed?

Thankfully there are two medical treatments for very heavy flow that have been shown to be both safe and effective in controlled trials. The first is the use of tranexamic acid, a medication that acts to increase the blood clotting system and decreases flow by about 50% (11). The second is a progestin-releasing IUD called “Mirena®” that decreases flow by about 85-90% (12). Both of these, studied over years, are nearly as effective as endometrial ablation, the surgical scrapping or destruction of the uterine lining, in controlled trials. Either of the emergencies therapies, tranexamic acid and Mirena®, should be used with cyclic normal dose progesterone, ibuprofen and extra salty fluid if needed.

Wrapping up section

In summary, very heavy menstrual bleeding means soaking 12 or more regular sanitary products in one period. About 25% of women in very early perimenopause or early menopause transition, some teens and a few women of other ages will experience this. No matter at what age heavy flow occurs, using a menstrual cup will help prevent embarrassing leaks and allow less frequent visits to the washroom. At present more than 50% of North American women with very heavy flow end up with a hysterectomy that can almost always be avoided. Very heavy flow can be helped by ibuprofen (1-2 tablets with every meal on every heavy flow day), extra salty things to drink, increasing dietary or supplemental iron and with cyclic progesterone or medroxyprogesterone. If flow is heavy in perimenopause progesterone will need to be taken daily for three months. Finally, a strong progestin-releasing IUD, Mirena® has been shown to be effective for both heavy flow and for contraception.


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  2. Cole SK Sources of variation in menstrual blood loss. J Obstet Gynaecol Br Commonw 1971; 78:933.
  3. Allen DG. Abnormal uterine bleeding and cancer Aust N Z J Obstet Gynaecol 1990; 30:81.
  4. Santoro N. Reproductive hormonal dynamics in the perimenopause. J Clin Endocrinol Metab 1996; 81:1495.
  5. Prior JC. Perimenopause: Endocr Rev 1998;19:397.
  6. Prior JC.Ovulatory changes with perimenopause. Novartis Found Sym 2002; 242:172.
  7. Fraser IS Treatment of menorrhagia with mefenamic acid. Obstetrics and Gynecology 1983; 61:109.
  8. Casper RF MinestrinTM on vaginal bleeding patterns in symptomatic perimenopausal women. Menopause 1997; 4:139.
  9. Preston JT Tranexamic acid and norethisterone in the treatment of ovulatory menorrhagia. Br J Obstet Gynaecol 1995; 102:401.
  10. Irvine GA. Randomised trial of the levonorgestrel intrauterine system and norethisterone for menorrhagia. Br J Obstet Gynaecol 1998; 105:592.
  11. Bonnar J Treatment of menorrhagia BMJ 1996; 313:579.
  12. Marjoribanks J Surgery versus medical therapy for heavy menstrual bleeding. The Cochrane Database of Systemic Reviews 2003; 3:1-65.
  13. Casper RF, Dodin S, Reid RL, Study Investigators. The effect of 20 µg ethinyl estradiol/1 mg norethindrone acetate (Minestrin™, a low-dose oral contraceptive, on vaginal bleeding patterns, hot flashes, and quality of life in symptomatic perimenopausal women. Menopause 1997; 4:139-147. 
Dr. Jerilynn C. Prior, Scientific Director, Centre for Menstrual Cycle and Ovulation Research
Updated Date: 
October 4, 2017

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